1. Field of the Invention
This invention relates to a rotation detecting apparatus for obtaining an output voltage in proportion to the rotation speed of a rotary machine.
2. Description of the Prior Art
Up to now, various rotation detecting apparatuses have been proposed which are used to control a rotary machine at a constant speed or to measure the rotation speed of a rotary machine or the like. However, most of them had the defects such that a ripple voltage was included in a proportional output value at the time of rotation at a low speed or that the response property for speed was poor.
A conventional example is shown in FIG. 1A. By the rotation of a rotary machine 1, a frequency signal is generated from a power generator 2 and input to an amplifier 3. The output signal of the amplifier 3 is input to a waveform shaping circuit 4 and formed to a square wave, by which a monostable multivibrator 5 is triggered. The output signal of the monostable multivibrator 5 is smoothed by an integrating circuit 6. This comparatively small amplitude smoothed signal is amplified by a DC amplifier 7 to drive the next stage and to drive a rotation speed indicator 8. If the above-mentioned rotary machine 1 is, for example, a DC motor, by providing the above-mentioned DC amplifier 7 with a reference voltage generating circuit and a comparator for comparing this reference voltage with the smoothed signal from the above-mentioned integrating circuit 6, it will be possible to control the supply voltage of the motor and to maintain the rotation speed at a predetermined constant value.
FIG. 1B shows the signal waveforms at each section in the above-mentioned conventional example, indicating the states in which the rotation speeds increase gradually. Assuming that the source signal from the power generator 2 is a sine waveform, the output signal waveform of the amplifier 3 is as shown by S.sub.1 and after waveform shaping, by S.sub.2. By triggering the monostable multivibrator 5 on the rising section of the square shaped signal S.sub.2, the output signal waveform of the monostable multivibrator 5 becomes a pulse waveform of which the repetition period T decreases along with the time t as shown by S.sub.3.
Signal S.sub.4 is the signal of pulse waveform S.sub.3 smoothed, the voltage of which increases gradually. In the above-described example, a change of speed is detected each repetition period T in the case of signal S.sub.3. Therefore, it is necessary to hold the preceding detected value before the next pulse waveform is applied and it is impossible to detect a change of speed in at least the holding period. Due to this the last stage signal becomes a staircase waveform like S.sub.4 ; thus, it includes ripple. Furthermore, since the repetition period T exists, there is a defect that the time lag becomes large easily. This time lag and the including rate of the ripple component for the signal are significant especially at low speed rotation, that is, when the repetition period T is large.
It is necessary to satisfy the following conditions to obtain a DC output in response to the rotation speed with no defects as described above.
First, the ripple voltage which has no relation to the rotation speed must not be included in the output voltage. Second, there is a proportional relationship between the rotation speed and the detected signal. Third, good responsiveness must be obtained. Fourth, a sufficient detected signal must be obtained even at low rotational speed. In addition, the rotating direction must also be discriminated.
Although small power generators of the multi-phase rectifier type have been used generally to meet the above-mentioned conditions, there are defects such that there is a problem of durability because when the rectifier is used, electrical and mechanical noises are generated, and a multiple-winding armature must be used inevitably to reduce the ripple voltage component of the output voltage, so that the apparatus becomes complicated and expensive.
It is therefore an object of this invention to provide a rotation detecting apparatus in which by using a power generator with a magnet as the rotor, the number of phases of the armature coils is reduced by eliminating the rectifiers and brushes, and at the same time good responsiveness of the rotation speed output voltage is obtained by using an electric circuit having a special construction and the unnecessary ripple voltage is eliminated, thereby getting rid of the above-described defects.